1. Field of the Invention
The invention generally relates to a power converter, and in particular relates to multiple power converters running in parallel and synchronously.
2. Related Art
In conventional power converters, parallel circuits are used to increase the current output while preventing from power loss and heat generation caused by current increasing on each circuit.
As shown in FIG. 1, a power converter of prior arts includes a pulse-width modulator 10, a first transistor TR1, a second transistor TR2 and an inductor L1. The drain terminal of the first transistor TR1 is connected to the power source Vdd. The source terminal of the first transistor TR1 is connected to the drain terminal of the second transistor TR2. The source terminal of the second transistor TR2 is connected to the ground. The pulse-width modulator 10 provides an oscillating pulse to the gates of the first and second transistors TR1, TR2 via a first resistor R1 and second resistor R2. When the pulse of the pulse-width modulator 10 is at the positive cycle, the first transistor TR1 is on and the second transistor is off; a current flows through the first transistor TR1 to the first inductor L1, as the illustrated path P1, and stored energy in the first inductor L1. When the pulse of the pulse-width modulator 10 is at the negative cycle, the first transistor TR1 is off and the second transistor is on; the first inductor L1 releases energy through a reversed path P2. Therefore, the first inductor L1 is charged and discharged corresponding to the pulse oscillation, and provides a stable current to a CPU 70. A capacitor C1 is connected between the power input and the ground of the CPU 70 for voltage regulation.
In the power converter circuit of FIG. 1, the inductor L1 provides a current I to the CPU 70. If the CPU 70 requires twice of current 2I, then another power converter has to be added in parallel as shown in FIG. 2, in which a third transistor TR3, a fourth transistor TR4, a third resistor R3, a fourth resistor R4 and a second inductor L2 are linked and function in the same way of FIG. 1. The current output of the first inductor L1 is I1. The current output of the second inductor L2 is I2. If I1=I2=I, then the total current output It=I1+I2=2I.
There is a limitation in the operation of the power converter of FIG. 2. That is, the pulse-width modulator 10 and the pulse-width modulator 20 have to work synchronously. Otherwise, the current outputs of the first inductor L1 and the second inductor L2 are unbalanced. Then, for a certain load of current It, one of the inductor L1 and L2 has to provide a larger current than the original current I that will cause overload of the components. For this problem, an additional current-balancing circuit has to be used for controlling the currents in both paths to the regular range.
As described above in FIG. 1 and FIG. 2, for controlling multiple power converters of prior arts, additional pulse-width modulators and current-balancing circuits are required, and the costs are increased accordingly. Therefore, it is a demand to have a simpler structure of power converter that has a lower cost for benefits to customers and the manufacturer.